Nitrox main tank.....air in pony...?

[RICHinNC]

A while back I did a thread about the pros and cons of diving nitrox (32%) but using an air computer. The idea was......a lot of people say they are less tired with nitrox....and using an air computer would add an additional safety margin. There was a lot of good discussion on that. (my lds hates nitrox and when I asked the question there, the owner indicated it is the only way he would recommend diving nitrox)

But, my question here is.......if one does dive nitrox in the main tank.....is it ok to still just have "air" in a pony bottle? And, when I say pony bottle I dont mean a deco stage bottle.....just a small 13 cu ft bail your butt out of a jam bottle.

Would switching to the pony in an emergency and breathing air after having breathed nitrox for a while cause any problems?

(my thought is it wouldnt....you breath "air" when you surface, but there might be something I am missing there.)

[blackice]

I'm no expert at all .. but I would think it's fine to switch to air as air has a deeper MOD than Nitrox mixes. So there would be no decom issues, it would be mainly a matter of nitrogen loading and how you go about assessing it.

Interesting to hear what others say...

[salty]

why not just put 28% in your pony and not worry about it?

[Diversauras]

RICHinNC once bubbled...
A while back I did a thread about the pros and cons of diving nitrox (32%) but using an air computer. The idea was......a lot of people say they are less tired with nitrox....and using an air computer would add an additional safety margin. There was a lot of good discussion on that. (my lds hates nitrox and when I asked the question there, the owner indicated it is the only way he would recommend diving nitrox)

But, my question here is.......if one does dive nitrox in the main tank.....is it ok to still just have "air" in a pony bottle? And, when I say pony bottle I dont mean a deco stage bottle.....just a small 13 cu ft bail your butt out of a jam bottle.

Would switching to the pony in an emergency and breathing air after having breathed nitrox for a while cause any problems?

(my thought is it wouldnt....you breath "air" when you surface, but there might be something I am missing there.)

Firstly, I love nitrox and only dive air when I can't get it. Even offshore in NC I do 30%. I also let my computers know what I am diving in order to maximize the benifits from the reduced nitrogen.

Why does your LDS hate nitrox? Don't sell it, but the competition does?

That said, you question could be a loaded one. If you are using computer settings for the mix you're diving, and you have a deco obligation on you computer, then switching to air could be a problem because you won't outgas at the rate your computer is calculating.

If you use the pony bottle air to complete any dive, deco or not, if you are using mix settings instead of air settings on your computer, then you computer doesn't know where you are.

It seems to me that a higher mix in the pony would make more sense. If you had to use it at depth, below it's MOD, the exposure would be minimal because you would be in ascent. If the O2 is a higher mix than your computer has set then what is being fooled is the O2 clock. I would use a higher mix, say 40%.

[japan-diver]

Don't quite understand the LDS not liking nitrox - sounds like someone stuck in the dark ages.

If you are diving Nitrox but left your computer on air, than having air in the pony is a mute question as the computer assumed you were diving air the whole time anyway. There is no problem with switching during the dive.

I have to disagree with putting a higher mix in the pony if there is a chance of exceeding the MOD as it only takes a few breaths for a CNS hit and there is no reason to put yourself at this risk no matter how small the risk is. I would reccomend the same mix as is in your main tank.

[Genesis]

is that you will have an incentive to ALWAYS get it topped off.

A small pony is not good if its not FULL. And I do mean FULL!

A 13cf pony is BARELY big enough to be useful. If its down 500 psi, its a lot less useful, perhaps enough to make the difference between making it and not.

A pony is not the "right device", in general, for deco diving. It doesn't have enough gas to cover you if you have a problem with the main tank, which is NECESSARY or your NEXT pony ride will likely be of the iron variety!

But for NDL diving, yes, air in the pony is just fine, PROVIDED that you immediately call the dive when you pull it, AND you either end your diving day when you use it OR are EXTREMELY conservative from that point forward (better to call the diving day) as your computer's tissue loading numbers will be a bit off.

With that said, if your shop BANKS Nitrox, then topping a pony with 32% is pretty easy, and if that was the case (I had banked 32%) I'd fill and top the pony with that instead. 32% is ok to breathe down to 130 in a pinch (1.6 PO2) which will cover you to basically any recreational depth.

If your shop PP mixes their Nitrox then topping a pony is a pain in the butt and usually involves partially or totally dumping the existing gas. That gets out of hand fast and the shop is going to charge you for a fill, as its not just a couple of cf nor is it nearly as quick. In that case I'd fill it with air.

[RICHinNC]

Maybe I wasnt quite clear enuf....

The pony is a pure bail out....total main failure...last resort thing. There would be no need ever to finish a dive with a 13 cuft pony with good air usage monitoring.

As to why my lds hates nitrox is hard to tell. He gets too emotional and hasnt really conveyed why to me. Plus, I dont think he wants to cost involved of offering nitrox as he is barely keeping his business head above water...sorry about the pun. The last time we did talk nitrox....and I asked this question....he was emphatic that if he ever dived...or recommended diving nitrox...it would be only with the use of an air computer following air limitations.

The comment about the % is interesting. I was in Ocean City MD a while back and stopped into an lds. We talked about nitrox and the owner said he never fills less than 40%. When I asked why not....he just gave me a disgusted look and commented that anyone filling under 40% needs to take a nitrox class. First of all I thought that you only could get nitrox IF you have taken a class. And, I thought the "standard" fills were 32 and 36 %.... that the 40% is the limit one can use before having to have DEDICATED equipment for nitrox only.......as it applies to non tek fills.

As for keeping the pony filled with say a 32% blend is an interesting thought. My questions there would be.... what is the effect on valves and regs with relative long term storage with nitrox??? I usually fill my pony at the beginning of my dive season....breath off it once or twice to check it out each dive....top it off after every 3rd or so dive.....and drain during the off season. Would it be worth while to do nitrox that way in a pony.

Since I have been curious about this, no one in my discussions has come up and given any definitive comments and reasoning. Which in itself I find pretty interesting. It could be because no one has done any studies around this subject. But it makes me wonder what they know definitively about anything else they seem to be experts on. Just the cynical side of me sneaking out!!

Appreciate your responses.

[O-ring]

Definitely something low o2 so you can have more depth flexibility.

[Genesis]

No issues with keeping 32% in a tank.

Consider that the 100% O2 that comes in my supply tanks has an expiration date of several YEARS from the date of production (typically 3 or so.)

If you can get banked Nitrox, fill it with that. If not, then fill it with air. Its far more important that you keep it FULL than what gas is in there, provided its BAIL OUT ONLY.

If you EVER are tempted to breathe it as a "dive extender", then you need to disabuse yourself of that notion rather than trying to allow for it somehow.

[Doc Intrepid]

1. You're on the way to the surface.

2. You're diving No-Decompression Limits, under recreational circumstances.

3. Depending on the depth at which your "Oh $hit" occurs, you'll be breathing off the contents of the tank for little more than two minutes (at a recreationally-oriented ascent rate of 60' per minute, which is two minutes to the surface from 120').

4. With only 13 cu ft to begin with, and hyper-awareness and elevated respiration rate resulting from your "Oh $hit", whether or not you'd have enough in the pony for a 3 minute safety stop is rather academic.

5. It's irrelevant whether you have air in it or EAN during a 2 minute straight shot ascent.

So put air in it.

Doc



P.S. What about your buddy? Use his Nitrox.

[nyresq]

Putting a nitrox mix in it now sets an MOD (maximum operating depth) within rec limits that CAN NOT BE VIOLATED. People have died breathing the wrong mix for their depth. As stated prior "its just for a few breaths" can throw you into a siezure from a cns hit. Because it won't be "just a few breaths" if you need to go to your bail out bottle. The Sh3t hits the fan, you WILL start breathing harder and you will lower your resistance to a cns hit while trying to get out of trouble. A ppo2 of 1.6 or 1.7 is ok if your just cruising along at a nice comfortable pace and are relaxed. but get excited and flustered and all of a suden that quick hit of a rich mix will throw you into a siezure, and then its goodnight... forever.

fill it with air and you're good to a MOD of 220'. and you can get it filled anyplace you go, you won't need to worry about getting it filled at a local shop on a boat or at the quarry etc...

As far as deco, you've already said you're using an air (21%)computer, so there is no problem with nitogen loading/off gassing computations being different than your backgas.

You've already said this is strictly a bail out/ run for home pony, but IMO I think 13 is too small. At 120' 13 cuft will not last very long. Do a search on pony size and read a few threads on this. I remember one of the threads had calculations worked out for size vs depth vs time needed to surface safely. you might be quite suprised how little time a 13 cuft will last at depth. For the extra gas I think a 20 cuft is worth the small (couple of inches length) increase in size.

[Genesis]

on deep dives I carry a 19cf bottle.

If that's not enough, its time for doubles.

[ColdH20diving]

Genesis once bubbled...
on deep dives I carry a 19cf bottle.

If that's not enough, its time for doubles.

ditto, I was considering using a higher O2 concentration in my pony bottle as I don't have an oxygen set up on the surface.... yet, but since the only way to deliver it would be via a demand system I didn't think it was worth it.

[Genesis]

is don't get tempted to use it to extend bottom time. Ever. Not even once.

[doctormike]

I agree with the previous comments about the nature of at pony bottle and when it should be used... in most situations (e.g. not close to the EAN deco limits), switching to air wouldn't make too much of a difference. You would also need a dedicated nitrox pony to allow for safe filling.

I also think that the standard line about diving nitrox using air tables/computers to reduce DCI risk is that it doesn't really make much of a difference. DCI risk following air tables is really very low, and switching to Nitrox doesn't make a statistically significant difference, IMO. Nitrox (as most people here know) is to extend non-deco time within a fairly limited depth range up to the MOD of the mix that you are using, nothing more (not to "feel better" after diving).

[DivingGal]

DeepTechScuba your post "RIDING THE PONY " provides a weath of information. Not only the whats, but also the whys and how.

Bravo.

(BTW -- I've only put air in my pony. I've used (1) to fill a lift bag a couple of times and (2) as a bail out when my buddy had a problem with her air. )

[evad]

Genesis (what he said). So if I'm probably not going to drift deeper than 120 fsw (PO2 1.5) in an emergency and I can get 19cf pony topped off with banked ean32 sold by the cf for about the same price as air, why would I not use the ean32 ? Only because its not necessary? Thanks. Deadly curious sophomore diver.

[medic13]

for off shore diving I use EAN 30 for main and EAN 32 for pony
but feel just as cofortable using air in my pony as its for a back up and emergency only not diving it .
remember the rules of third and you should have plenty of air for your PLANNED DIVE , stick to your plan and dive your plan if at all possible .again my two cents

[RICHinNC]

IM BACK>>>
Well I took my Enriched Air course this weekend. The instructor and I talked extensively on why I was taking the course... my thoughts on how I would employ enriched air....what type of computer I would use....and the question about the pony.

As far as the pony goes....it is exclusively for use in an emergency situation only....cant find or get to buddy...had a main failure...headed right up. In the instructors opinion...use of standard air in a pony is certainly acceptable. He also reiterated a couple of comments here...dont use it to extend the dive...and if the thread was well read...it should be obvious that was not the intention. He did note, if I fixed whatever the problem was that caused the use of the pony...to sit down with the tables and figure what the oxy exposure would be using the two gasses.

Now my lds main man....is very anti using the same gear I dive regular air with. He is adamant that I should have all seperate nitrox dedicated gear. And, I really think he feels that way because of safety and his thoughts about nitrox....versus just trying to sell more gear.
It has been an interesting weekend.

[medic13]

congrats on your course personally i dive nitrox almost all the time .
wear you all at the quarry this weekend and how that go , what was the temp and visibility like .
looking for a dive for next weekend thinking of diving the Governor coastal scuba next weekend .

[nyresq]

Now my lds main man....is very anti using the same gear I dive regular air with. He is adamant that I should have all seperate nitrox dedicated gear. And, I really think he feels that way because of safety and his thoughts about nitrox....versus just trying to sell more gear.

Unless your shop has two compressors, one for nitrox and one for air (which I have never seen) the air your getting from an air fill is the same air that the shop uses to make the nitrox... the only reason for a nitrox specific reg would be if you get air fills at some place that your not sure of the quality of air and don't want to risk contaminating your reg... but then in that case your also going to need a different tank also, dirty air contaminates a tak faster then regs... unless you plan on diving nitrox for deco gases (higher than 40%) you don't need a dedicated nitrox reg.
Your LDS has no basis for this recomendation if your fills (air and nitrox) are coming from only them. Air for air fills and air for mixing nitrox is coming out of the same machine...

Just for fun, tell your LDS you've taken his advice and purchased a nitrox reg from another LDS and see what he says...

save your money...:out:

[RICHinNC]

Medic...yep it was at Fantasy Quarry in Raleigh. The vis was like zip...terrible...waste of time....but I needed the two dives for the card.
It really was a riot. The instructor and I jumped in...I told him he knew the quarry better than me...just swim around long enough to meet the requirement and lets get the heck out. The water was like ice and all i had brought was my 3/2.....NOT GOOD>

So in we go and there were two other guys already in just about to go under. We all sink down and it is real obvious...cant see squat. We finally link up and off he goes with me glued to his side like a new born dolphin....

We get to the crusher, I think, and he goes in....I dont...I cant see anything....my mask is leaking because I didnt trim my beard well and Im thinking no way I am going in. So I circle up on top until "he" comes up and motions to move on. So I move on...only it wasnt him. It was one of the other guys who thought I was his buddy. They had gotten sepearated. \

So off we go. What I find out later is....the instructor comes out of the crusher and links up with the other dude thinking it was me and off they go.
Somehow we all get seperated again....like i said...the vis super sucked......

Im down there thinking....dang...after all that blessed math I just went through Im gonna flunk this course because we got seperated!!!

So up I go. It was a riot. Everyone had the same idea at the same time. I break surface just as one of the other dudes do and immediately realize it aint david the instructor...i go...who are you....he goes who are you....way off i hear...im over here...
what a zoo!!

We did the second dive without incident and david
said keeping track of your buddy wasnt part of the course requirement (now keep your flames to yourselves....he was trying to maintain a sense of humor..)

So I passed the course....literrally froze to death...and it takes a lot to make me cold...then spent an hour on 440 because of stalled traffic. Left Fayetteville at 6 am...got home at 9 pm. Duh!!

[medic13]

well I had wanted to go up there but to be honest I was booked for a double shift two 24 hrs shift total 48 this weekend and had a friend of mine die this past week .
http://www.scubaboard.com/showthread.php?s=&threadid=39147

anyway other than that would of been there I know the quarry well was part of my compass course and friend took his DM traing out there we practiced compass courses and even mapped allot of it out so I have most of the spots marks with feet ect ect ect . but other than cold better diving than day on the land lol luckly not that cold off coast lol and visability is better lol.

[evad]

He is adamant that I should have all seperate nitrox dedicated gear.



That seems rediculous. Find a place that has banked ean (not mixed in the tank) so you won't have to pay to have your tanks cleaned. You don't have to have your regulator cleaned either. That's at least $150.00 you don't need to spend until you do advanced nitrox.

[Norm]

While I'm a firm believer in having the same gas in both tanks, what you are saying is probably alright. Just keep in mind that IF you are pushing the nitrox tables, (which no one should EVER do), I suppose there could be a problem.

[pt40fathoms]

One more voice for the chorus here.

Your pony bottle is a bail out device.

You will be using it to make a safe assent from depth during an emergency and that is the extent of its purpose.

Having it filled with air will in no way harm you. Provided you are not deep into a decompression dive profile, and do not have enough air in the pony bottle to safely complete all your decompression obligations.

So, fill it with air, and ensure it is of sufficient size to act as a bail out source of breathing gas for the dive profile you intend to dive. As an added measure of safety, practice using the pony bottle from a safe depth (30 - 60 feet) as often as practical, so the use becomes second nature and will be a reflex action in an emergency.

Oh, and make sure you let your buddy know you plan on doing a bail out drill on the dive so he won't freak out. :eek:

[domino22]

Was looking at a 6cuft pony with air to mount on the fwd side of my backplate under the right arm. I was looking at the 6 cuft because of size and for travel. If I travel alone ie most of the time I tend to get buddied up with a "Unkown person". I dive nitrox if available. I was wondering if the 6 cuft would be enough to get me up? I have a 19 cuft but it is to big for travel IMHO. I went to the BP&Wing for travel size. My normal depth is 80ft and less and I prefer around 60ft to 40ft for photos. I stay away from deco I am old. And like more bottom time for photos since I went digital. I suck at math so say from 80ft will the 6cuft pony save me-bend me or kill me?

[Don Burke]

domino22 once bubbled... Was looking at a 6cuft pony with air to mount on the fwd side of my backplate under the right arm. I was looking at the 6 cuft because of size and for travel. If I travel alone ie most of the time I tend to get buddied up with a "Unkown person". I dive nitrox if available. I was wondering if the 6 cuft would be enough to get me up? I have a 19 cuft but it is to big for travel IMHO. I went to the BP&Wing for travel size. My normal depth is 80ft and less and I prefer around 60ft to 40ft for photos. I stay away from deco I am old. And like more bottom time for photos since I went digital. I suck at math so say from 80ft will the 6cuft pony save me-bend me or kill me? Figure that 6 cuft bottle will last you about one fourteenth what the 80 cuft bottle lasts.